Polyvinylamine polymers comprise primary amine groups attached to the polymer structure or linear polymer backbone. The primary amine groups make the polymers highly reactive, and they are used in numerous applications, also in papermaking, because of their charge density, reactivity and water solubility. However, polyvinylamine polymers having high molecular weight may be too reactive, which may lead to overflocculation and problems in dewatering and retention in the wet-end of a paper machine or board machine.
In paper and boardmaking the use of inexpensive fibre sources, such as old corrugated containerboard (OCC) has been increasing over the past decades. OCC comprises mainly used recycled unbleached or bleached kraft pulp fibres, hardwood semi-chemical pulp fibres and/or grass pulp fibres. OCC pulp may be used especially for manufacture of liner and fluting grades, often together with mixed waste recycled paper grades. Consequently chemical additives, which are suitable for use with pulps comprising recycled fibres, are in constant demand.
EP 1 727 938 discloses a process for production of paper, board and cardboard in presence of polymers which comprise vinylamine units. The used polymers have an average molar mass of at least 1 million and a degree of hydrolysis of from 1 to 20 mol-%. The polymers are metered to high consistency stock which is diluted and drained. The stock may contain coated broke and disturbing substances originating from the coating. However, there is a still need for papermaking agent compositions which are especially suitable for improving retention and/or drainage of fibre stock comprising recycled fibres, especially fibres from old corrugated cardboard (OCC). Further, it would be advantageous if the chemicals used for retention and/or drainage would have a positive effect on the properties of the produced paper, e.g. burst strength, short span compression (SCT) and/or tensile strength.
One problem has been that the polyvinylamine polymers may neutralize all or most of the anionic charges in the short loop white water circulation of the paper or board machine. This may lead to the overcationisation of the fibre stock, which results in foaming, decreased dewatering effectivity and decreased strength properties in the final paper or board.